pgsql: Refactor broken CREATE TABLE IF NOT EXISTS support.

Refactor broken CREATE TABLE IF NOT EXISTS support.

Per bug #5988, reported by Marko Tiikkaja, and further analyzed by Tom
Lane, the previous coding was broken in several respects: even if the
target table already existed, a subsequent CREATE TABLE IF NOT EXISTS
might try to add additional constraints or sequences-for-serial
specified in the new CREATE TABLE statement.

In passing, this also fixes a minor information leak: it's no longer
possible to figure out whether a schema to which you don't have CREATE
access contains a sequence named like "x_y_seq" by attempting to create a
table in that schema called "x" with a serial column called "y".

Some more refactoring of this code in the future might be warranted,
but that will need to wait for a later major release.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/68ef051f5cf16f82a5368067a40ffba3c340b0d3

Modified Files
--------------
src/backend/bootstrap/bootparse.y  |    3 +--
src/backend/catalog/heap.c         |   19 +++----------------
src/backend/catalog/namespace.c    |   29 +++++++++++++++++++++++++++++
src/backend/catalog/toasting.c     |    3 +--
src/backend/commands/cluster.c     |    3 +--
src/backend/commands/tablecmds.c   |   29 ++++-------------------------
src/backend/executor/execMain.c    |   12 ++----------
src/backend/parser/parse_utilcmd.c |   32 ++++++++++++++++++++++++++++----
src/backend/tcop/utility.c         |   18 ++----------------
src/include/catalog/heap.h         |    3 +--
src/include/catalog/namespace.h    |    1 +
11 files changed, 73 insertions(+), 79 deletions(-)